PHP 5 >= 5.4.0, PHP 7, PHP 8
header_register_callback - Call a header function
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header_register_callback( callable$callback ): bool

Registers a function that will be called when PHP starts sending output.

The callback is executed just after PHP prepares all headers to be sent, and before any other output is sent, creating a window to manipulate the outgoing headers before being sent.



Function called just before the headers are sent. It gets no parameters and the return value is ignored.

Return Values

Returns true on success or false on failure.


header_register_callback is executed just as the headers are about to be sent out, so any output from this function can break output.


Headers will only be accessible and output when a SAPI that supports them is in use.

Related Functions

Example of header_register_callback

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